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Math Expert V
Joined: 02 Sep 2009
Posts: 55262
The average marks obtained in a test by x students of a class was m.  [#permalink]

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Difficulty:   85% (hard)

Question Stats: 35% (02:23) correct 65% (02:44) wrong based on 37 sessions

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The average marks obtained in a test by x students of a class was m. Was (x + 3) the average marks obtained by three students with the lowest marks in the same test?

(1) If the lowest three marks were excluded, the average score of the class would have increased by three.
(2) m = 2x.

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Manager  S
Joined: 02 May 2016
Posts: 77
Location: India
Concentration: Entrepreneurship
GRE 1: Q163 V154 WE: Information Technology (Computer Software)
Re: The average marks obtained in a test by x students of a class was m.  [#permalink]

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Bunuel wrote:
The average marks obtained in a test by x students of a class was m. Was (x + 3) the average marks obtained by three students with the lowest marks in the same test?

(1) If the lowest three marks were excluded, the average score of the class would have increased by three.
(2) m = 2x.

C ?

My understanding:

B doesnt help.

Using A:
say Sum of All/No Of Students=A/x=m
So A=mx.
Say Sum of lowest 3=L.
\frac{A-L}{x-3}=m+3
A-L=(x-3)(m+3)
A-L=mx+3x-3m-9
Use A=mx and change sides
L=3m-3x+9
L is sum of lowest 3, its average will be L/3=(3m-3x+9)/3= m-x+3
m could be anything, so Not sufficient.

Using m=2x from B,
L/3=2x-x+3=x+3
Sufficient. DS answer C.

BUT I believe if C is the answer then there might be some kind of trap making A/B/E the answer. Couldn't find the trap.
Waiting for OA and OE by expert!
Intern  B
Joined: 11 Apr 2017
Posts: 5
GMAT 1: 740 Q51 V39 GPA: 4
Re: The average marks obtained in a test by x students of a class was m.  [#permalink]

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C??

From 1 we can get that average marks obtained by three students with the lowest marks in the same test = (m-x)+3.

We have no Information about the relation between m&x and it may or may not be the case that m-x = x

2 doesn't help individually.

Combining 1 & 2 we get Average marks obtained by three students with the lowest marks in the same test = (m-x)+3 = (2x-x)+3 = x+3.

Hence C should be the answer.
Senior Manager  G
Joined: 06 Jul 2016
Posts: 363
Location: Singapore
Concentration: Strategy, Finance
Re: The average marks obtained in a test by x students of a class was m.  [#permalink]

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1
Bunuel wrote:
The average marks obtained in a test by x students of a class was m. Was (x + 3) the average marks obtained by three students with the lowest marks in the same test?

(1) If the lowest three marks were excluded, the average score of the class would have increased by three.
(2) m = 2x.

Average = $$\frac{Sum}{Number}$$ = $$\frac{S}{x}$$ = m
$$\frac{L}{3}$$ = x+3?

1) Lowest 3 marks = L
$$\frac{(S-L)}{(x-3)}$$ = x+3
=> S-L = mx+3x-3m-9
=> mx - L = mx+3x-3m-9
=> L = 3m-3x+9
$$\frac{L}{3}$$ = m-x+3
m = ?
Insufficient.

2) m = 2x
Doesn't help. Insufficient.

1+2)
$$\frac{L}{3}$$ = 2x-x+3 = x+3
Sufficient. C is the answer.
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Put in the work, and that dream score is yours! Re: The average marks obtained in a test by x students of a class was m.   [#permalink] 18 Jul 2017, 09:14
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# The average marks obtained in a test by x students of a class was m.

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